The purpose of the Epidemiology Project (Project 1) is to establish HIV incidence and risk factors for HIV infection in three regions of China in order to establish a foundation for conducting clinical trials of HIV prevention and therapeutic interventions. The three specific aims of Project 1 are: Aim 1: To estimate the prevalence and incidence of HIV-1 infection and selected sexually transmitted diseases over time in: a) former plasma donors (FPDs), their stable sexual partners, and their children in rural areas of Shanxi province; b) injection drug users (IDUs) and their stable sexual partners in rural areas of Yunnan Province; and c) female sex workers (FSWs) in Kunming, Yunnan Province; Aim 2: To determine risk factors for HIV infection in the above population, and to recruit participants from these populations for participation in cohort studies in preparation for vaccine, behavioral and therapeutic intervention studies; and Aim 3: TO estimate the prevalence and incidence of HIV-1 infection, HHV8 infection and co-infection with HIV-1 and HHV8 in high risk minority population in Xinjiang Province, and to determine factors that are independently associated with co- infection with HIV-1 and HHV8. Strategies for recruitment and retention of study subjects will vary by study populations. About 1680 FPDs and 900 spouses will be recruited from 12 villages in Shanxi. About 600 HIV-FPDs or HIV-spouses will be followed in year 3 and 5. About 960 IDUs and 400 spouses will be recruited from 48 villages in Yunnan. About 504 HIV-IDUs and some 250 HIV-spouse will be followed at 6, 12, 18, 24 and 30 months after baseline. About 1000 FSWs will be recruited in hotels, entertainment establishments, and in the streets of Kunming City, Yunnan. FSWs will e followed for 2 years with 3 months interval contract and 6-month interval for assessment. About 250 subjects each will be recruited from Kelkez, Kazak, Ughur and Han ethnic groups and followed annually in Urumi, Xinjiang Four biologic indicators (HIV, gonorrhea, chlamydia, and syphilis) will be used cross all 4 study populations. HHV8 will be additionally used in study of minorities in Xinjiang. Our FPD and IDU studies will provide a subject of subjects (HIV positive) for the behavioral intervention study planned in Project 2. In collaboration with Project 4, we will seek to provide clinical care for HIV infected persons identified over the course of recruitment. We will provide clinical specimens for key research initiatives described in Projects 3 and 4. Planning for field trials or candidate HIV vaccines will link Projects 1 and 5.